Self-igniting internal combustion engines are usually equipped with heating pins to facilitate the ignition of a fuel-air mixture inside the combustion chamber in a cold start. The control of the heating pin continues even immediately following a startup of the engine, until the engine has heated up sufficiently so that the ignition may take place automatically without any additional heating of the air-fuel mixture.
At present, once the engine has been started, the heating pins are adjusted with the aid of a characteristics map, as a function of the cooling water temperature, the atmospheric pressure of the environment, and as a function of the number of engine cycles following the startup of the engine. However, the optimum afterglow temperature depends on the quality of the fuel used, the vehicle model in which the internal combustion engine is installed, and on constructional tolerances of the engine such as the clearance between the fuel jet injected into the combustion chamber of the engine, and the heating pin.
The glow temperature to which the heating pin is heated has a considerable effect on the service life of a heating pin.
Therefore, following the engine start, the glow temperature is usually reduced according to the mentioned characteristics map in an effort to extend the service life of the heating pin. Since the characteristics map must take into account possible constructional tolerances of the engine, different fuel qualities and different types of motor vehicles in which the engine is installed, in some internal combustion engines the afterglow temperature of the heating pin tends to be set higher than actually required for the proper course of combustion process, the adjustment being made via the characteristics map.